Tuberculosis continues to be a major disease and the single greatest infectious cause of human mortality. Several antigens of Mycobacterium tuberculosis, identified by monoclonal antibodies, have been cloned and are being exploited in the development of improved vaccines and diagnostic reagents. One of these antigens, the 16-kDa antigen, shows sequence homology with alpha-crystallin related small heat shock proteins. We have cloned the cDNA of this protein into the pet-20b+ expression vector to facilitate structure-function studies. Site-directed spin labeling will be used to elucidate the tertiary and quaternary structure of this protein.